Fiber reinforced resin assembly

ABSTRACT

An uncured fiber reinforced assembly that includes a reinforcement layer containing a fibrous material and at least one highly reactive curing agent. A matrix film layer is applied to the reinforcement layer so that it does not substantially impregnate the reinforcement layer. The matrix film layer includes at least one uncured epoxy resin and at least one latent epoxy curing agent. The assembly is designed for use in making snowboards and skis.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fiber reinforced resin assembly.

2. Description of Related Art

Fiber reinforced resin assemblies are widely used as structuralcomponents, in industrial and leisure applications. These assemblies aregenerally supplied as a prepreg. Prepreg materials comprise a fibrousreinforcement phase together with a matrix resin comprising one or moreresinous materials, one or more curing agents and optionally otheradditives such as accelerators, tougheners, flame retardants, fillersand the like forming together a so-called matrix resin. The matrix resincan generally be cured at temperatures in the range from 50° C. to 200°C.

The period of time in which a prepreg remains handleable with propertiesintact outside the specified storage environment, normally a cold storeor freezer, is called out-time or out-life. Known prepregs have limitedout-life in their uncured state at room temperature. This isparticularly evident in low temperature cure thermoset matrix resincompositions where the curing agents used to achieve cure at these lowtemperatures, typically between 50 and 100° C., react with the resinseven at ambient temperatures. For example, a matrix resin compositionconsisting of an epoxy resin and an imidazole curing agent that can becured at 60° C., can have a room temperature stability of less than twodays rendering it unusable thereafter. Stability during storage atambient temperatures is important, especially if materials are to betransported long distances, and/or stored at ambient temperatures beforeuse. It is, of course, possible to store these known prepregs attemperatures below room temperature to enhance their shelf-life, but theneed for large or expensive refrigeration units can make this optionundesirable.

For certain applications it is desirable that assemblies have anout-life of at least two weeks; this is particularly true where theassemblies find utility in sports applications, and more particularly inthe ski/snowboard industry. Furthermore, it is desirable that theassembly has a certain degree of tack. Tack, which is a measure of theadhesion of a prepreg ply to the tool surfaces or to other prepreg pliesin the assembly, is an adhesion characteristic of the matrix resin thatis controlled in order to facilitate ply cutting and lay-up operations.The plies should be capable of being removed and repositioned ifnecessary. For application in the ski/snowboard industry the assemblyideally has a tack level that is almost dry to touch, but the resin isflexible enough to permit the material to be wound around mandrelswithout cracking. The term “leathery” is sometimes used to describe sucha tack level. Several tests are available that can be used forsemi-quantitative measurement of tackiness. One such test uses a MeedusDatatac Analyser. This instrument consists of a sensor head assemblythat contains a precision load cell, which converts the tack force oneight sensor probes into an electric signal. A control console acceptsthis signal and processes it into stored analogue and digital peakvalues.

Attempts have been made to prolong the out-life of assemblies of thekind referred to herein. For example, U.S. Pat. No. 2,999,834 refers tothe application of a composition comprising a polymerization catalystembedded into a fibrous reinforcement. The matrix resin is then appliedto the fibrous reinforcement in situ such that the curing reactionoccurs. The catalyst is delivered to the fibrous reinforcement as adispersion or solution and therefore must not react with or initiate areaction of the solvent/dispersal medium. This clearly limits the natureof the catalyst that can be delivered in this way, which in turn limitsthe nature of the matrix resin. U.S. Pat. No. 2,999,834 also refers tothe application of a composition comprising the matrix resin and thecatalyst to a fiber reinforcement provided with a catalyst accelerator.In this instance the curing reaction is instantaneous and thus theout-life of the assembly is not prolonged.

EP 0424833 B1 refers to application of a metathesis catalyst to asubstrate. The substrate is then placed in a mold and a monomercomposition is applied to the substrate such that a curing reactionoccurs.

U.S. Pat. No. 3,666,615 refers to a composite sheet material comprisinga thermosetting resin layer and a hardening agent layer whereby the twolayers are separated by a contact preventative film that melts whenheated. A fiber base is embedded in either of the two layers to providestructural support for the composite. Thereby the room temperatureout-life of the assembly is prolonged. However, the use of such abarrier film requires using a film of a different type from thethermosetting resin, which complicates the system and increases thecosts and the time involved in producing the composite.

SUMMARY OF THE INVENTION

Thus, it is an object of the present invention to provide an uncuredfiber reinforced resin assembly for use in sports applications, and inparticular for the manufacture of ski/snowboard industry, which has anambient temperature out-life of at least two weeks and a ‘leathery’ tackto aid ply cutting and lay up operations, said tack preferably beingless than 15 pounds per square inch (psi) as measured by the Meedus tacktest.

According to a first aspect of the present invention there is providedan uncured fiber reinforced resin assembly comprising a fibrousreinforcement provided with at least one highly reactive curing agent,said fibrous reinforcement having a matrix film layer applied to atleast part of at least one of its surfaces wherein the matrix film layercomprises at least one epoxy resin material together with at least onelatent epoxy curing agent and wherein the matrix film layer does notsubstantially impregnate the fibrous reinforcement.

According to a second aspect of the present invention there is providedthe use in the manufacture of ski/snowboard equipment of an uncuredfiber reinforced resin assembly comprising a fibrous reinforcementprovided with at least one highly reactive curing agent said fibrousreinforcement having a matrix film layer applied to at least part of atleast one of its surfaces, wherein the matrix film layer comprises atleast one epoxy resin material together with at least one latent epoxycuring agent and wherein the matrix film layer does not substantiallyimpregnate the fibrous reinforcement.

With this arrangement, the advancement into the fibrous reinforcement ofthe components of matrix film layer is minimized such that the assemblyprovides the desired handling characteristics and out-life.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic cross-sectional view of one embodimentof an uncured fiber reinforced assembly of the present invention.

FIG. 2 is a partially schematic cross-sectional view of a furtherembodiment of an uncured fiber reinforced assembly of the presentinvention.

FIG. 3 is a partially schematic cross-sectional view of the uncuredfiber reinforced assembly shown in FIG. 1 after it has been cured toform a snowboard or ski.

FIG. 4 is a partially schematic cross-sectional view of the uncuredfiber reinforce assembly shown in FIG. 2 after it has been cured to forma snowboard or ski.

DETAILED DESCRIPTION OF THE INVENTION

As referred to herein, a latent epoxy curing agent is one that provideslong-term stability to a resin mixture at room temperature, but rapidcure at elevated temperatures. A reactive epoxy curing agent on theother hand, will cause undesirable rapid advancement of a thermosettingresin when stored at ambient temperature. As referred to herein, ambienttemperature is considered to be temperatures between about 10° C. and30° C. and more preferably 20° C. and 25° C.

Advantageously, the assembly of the present invention has an out-life ofat least two weeks. Clearly, this is highly beneficial to the transport,storage and use of the assembly. Furthermore, the assembly provides allthe necessary components to achieve a desirable composite upon curing.It is not necessary to add further polymer resins and/or curingagents/accelerators to the assembly in situ.

The assembly of the present invention possesses a ‘leathery’ tack idealfor the manufacture of skis or snowboards such that the preferred epoxyresin materials include bisphenol-A (BPA) and bisphenol-F (BPF) andderivatives thereof. Suitable epoxy resin material will preferably havea functionality of 2 and an epoxy equivalent weight (EEW) value in therange of 6.1 to 0.26 equivalents/kg and more preferably from 4.5 to 1.5equivalents/kg.

As referred to herein, by ‘does not substantially impregnate’ it ismeant that the matrix film layer preferably impregnates thereinforcement layer by less than 15%, more preferably by less than 10%and most preferably by less than 5%.

In order that the matrix film layer does not substantially impregnatethe fibrous reinforcement, the matrix resin materials therein have apreferred minimum viscosity of 100 Pas at ambient temperature. Thedegree of impregnation was determined by placing a matrix film layer ontop of a fabric layer positioned on a flat, smooth surface and leavingit for a period of days at ambient temperature. The impregnation levelcould be seen by taking observations over a period of days

The fibrous reinforcement may be based on synthetic or natural fibers,for example, fiberglass, carbon or aramid (aromatic polyamide) fibers,but the invention is particularly appropriate for fiberglass and carbonfibers. Hybrid or mixed fiber systems may also be envisaged. The use ofstretch-broken or selectively discontinuous fibers may be advantageousto facilitate lay-up of the product according to the invention andimprove its capability of being shaped.

The mass of fibers within the fibrous reinforcement is preferably in therange from 80 to 4000 g/m², more preferably in the range from 100 to2500 g/m², and most preferably in the range from 150 to 2000 g/m². Forcarbon based fibrous reinforcement materials, the number of carbonfilaments is in the range from 3000 to 320,000, more preferably in therange from 3,000 to 160,000 and most preferably in the range from 3,000to 40,000. For fiberglass reinforcements, fibers of 300 to 2400 tex areparticularly preferred. The fibers may be in unidirectional form, or asnon-woven form, such as multi-axial fabrics or non-crimped fabrics, ormay be present as a woven fabric or non-woven mat or fabric orcombinations thereof.

The highly reactive curing agent is preferably a solid at room ambienttemperature. Suitable highly reactive curing agents which may be usedalone or in combination include 2-methylimidazole, 2-ethylimidazole, butpreferably 2-phenylimidazole. Typically, the highly reactive curingagent is preferably incorporated into the fibrous reinforcement by wayof solvent evaporation. The highly reactive curing agent is dissolved ina suitable solvent, for example methylene chloride, acetone or methylethyl ketone. The fibrous reinforcement is then passed through a bathcontaining the curing agent solution. The solvent is subsequentlyevaporated off leaving the curing agent dispersed within the fibrousreinforcement.

Preferably, the latent curing agent(s) of the matrix film layer is analiphatic and/or aromatic amine that is solid at ambient temperature.The most preferred latent curing agent is dicyandiamide.

The matrix film layer may also include an accelerator, which istypically a urone. Suitable accelerators, which may be used alone or incombination include N,N-dimethyl, N′-3,4-dichlorophenyl urea (Diuron),N,N-dimethyl, N′-3-chlorophenyl urea (Monuron), but preferablyN,N-(4-methyl-m-phenylene bis[N′,N′-dimethylurea] (UR500). The matrixfilm layer may also include additional ingredients as performanceenhancing or modifying agents, for example flexibilizers, tougheningagents, accelerators, thermoplastics and core shell rubbers, flameretardants, wetting agents, pigments/dyes, UV absorbers, anti-fungalcompounds, fillers, toughening particles and viscosity modifiers. Thechoice of additional ingredients is dependent upon the desiredproperties of the assembly.

The matrix film layer typically comprises 25-45% of the combined weightof reinforcement plus matrix. The matrix film layer of the presentinvention is preferably applied to the fibrous reinforcement by a filmtransfer process thus providing the assembly described herein. Suchprocesses are well known to those skilled in the art. The curing agentsand accelerator are present in quantities sufficient to bring about curein the desired temperature range. Typically, these materials are allpresent at a level below 15 parts per hundred of resin.

The fiber reinforced resin assembly as hereinbefore described ismanufactured using processes well known to those skilled in the art.

Thus, according to a further aspect of the present invention there isprovided a method for curing a fiber reinforced resin assemblycomprising a fibrous reinforcement provided with at least one highlyreactive curing agent, said fibrous reinforcement having a matrix filmlayer applied to at least part of at least one of its surfaces, whereinthe matrix film layer comprises at least one epoxy resin materialtogether with at least one latent epoxy curing agent and wherein thematrix film layer does not substantially impregnate the fibrousreinforcement and wherein the said assembly is cured at a temperature inthe range from 80° C. to 150° C.

Preferably the fiber reinforced resin assembly resin assembly is curedat a press cure cycle of 3 minutes at 130° C. or 15 minutes at 100° C.Of course other press-cure cycles can be used. Thus, according to thefourth aspect of the present invention there is provided a compositearticle comprising a cured fiber reinforced resin assembly ashereinbefore described. Alternative cure cycles may be employed asappropriate. Vacuum bag and autoclave curing can also be utilized.

In order that the present invention is understood it will now bedescribed by way of the following examples.

EXAMPLE 1

Component Weight (%) LZ1523 77.40 DLS772 10.10 DYHARD 100SH 3.85 UR5004.80 2-phenyl-imidazole (2PZ) 3.85

LZ 1523 is an epoxy resin blend available from Huntsman AdvancedMaterials, Duxford, England. DLS 772 is a standard diglycidyl ether ofbisphenol-A, with a functionality (f) of 2, a molecular weight of 384and an epoxy equivalent weight of 5.2 equiv. per kg and is made byHexcel Composites Limited, Duxford, England. Dyhard 100SH is amicronized dicyandiamide; and UR500 is a urone curative, both obtainedfrom Degussa, Zurich, Switzerland. The imidazole is from Cornelius,Bishop's Stortford, England.

The imidazole, 2PZ, is incorporated into the fabric, while the othermaterials are all part of the resin matrix.

Preparation of the Matrix Component:

-   1. The Dyhard 100SH and the UR500 were dispersed in the DLS772 to    form a premix resin using a high-speed disperser.-   2. The LZ 1523 was charged to a Winkworth Z-blade mixer at ambient    and preheated to 60° C. The premix was added at this temperature and    the mix was blended until a uniform consistency was obtained. The    mix was subsequently decanted and stored at −18° C. until required.-   3. A resin film with a nominal weight of 310 gsm, approximating to a    resin content of 37% in the final assembly, was cast onto a release    paper using a hot roll coater.

Preparation of the Hardener Component:

-   4. A 4.5% solution of 2PZ imidazole in acetone was prepared. This    solution concentration ensured a nominal 13 g of reactive curative    was incorporated in each square meter of fabric.-   5. A stitched unidirectional 550 gsm glass fabric was passed through    a bath containing the solution from step 4 and subsequently through    two ovens to evaporate off the solvent. A surface fleece may    optionally be included in this assembly to minimize fiber tow    movement and to provide a smoother surface appearance to the cured    laminate.-   6. Finally, the film prepared in step 3 was lightly tacked onto the    surface of the 2PZ -impregnated fabric, ensuring minimum    impregnation into the fabric. A polyethylene or silicone coated    release paper may be placed as a protector layer on one or both    sides of the assembly. The assembly may be supplied in rolls or as    cut sheets.

Cure Characteristics:

The fiber reinforced resin assembly displayed suitable activity whencured for 15 minutes at 110° C. or for 3.5 minutes at 130° C. Glasstransition temperature (Tg) was used as a measure of the degree of cureof the cured laminates—rectangular DMA specimens, of nominal dimensions40×5×2 mm, were cut using a diamond tipped wheel Micar saw. Dynamicstorage modulus (E′) and damping (tan delta) were measured in a TAdynamic mechanical analyzer fitted with a single cantilever head.Dynamic scans were performed at a heating rate of 5° C./min over thetemperature range 50° to 275° C. at a frequency of 1 Hz. The results,shown below, and the thermal traces confirmed that the assembly hadcured and that it had suitable thermal performance for ski or snowboardcomponent production.

Tg (° C.) Tg (° C.) Cure Cycle Ext. onset E′ Tan delta peak  15 min. @110° C. 121 138 3.5 min. @ 130° C. 118 140

The out-life of the assembly was determined over a 14 day storage periodat room temperature. Assemblies were cured for 30 minutes at 100° C. andthe Tg and visual aspects of the laminates observed. The Tg showed nodrop in value over the storage period and visual inspection of thelaminates showed no evidence of voids due to lack of ply-consolidationand other imperfections associated with the processing of aged material.The Tg data indicates that the out-life of this assembly is a minimum of14 days. The out-life of a conventional fully homogenous prepreg madewith the same formulation would be less than 3 days.

No. of Days @ Room Tg (° C.) Tg (° C.) Temperature Ext. onset E′ Tandelta peak  0 (as made) 110 128  7 114 130 14 115 128

EXAMPLE 2

Component Weight (%) GY280 43.5 GT7071 43.5 DYHARD 100SH 4.0 UR500 5.02-phenyl-imidazole 4.0

GY 280 and GT7071 are both epoxy resins available from Huntsman AdvancedMaterials.

The imidazole, 2PZ, is incorporated into the fabric, while the othermaterials are all part of the resin matrix.

Preparation of the Matrix Component:

-   1. The GY280 and GT7071 resins were charged to a mixing tin and    preheated in an air-circulating oven at 80° C. The resins were    blended by hand.-   2. The tin was transferred to a oil bath preheated at 80° C. The    DYHARD 100SH+UR500 were charged to the tin and they were blended    into the resins using a mechanical stirrer. The tin was removed from    the oil bath and stored at −18° C. until required.-   3. A resin film with a nominal weight of 495 gsm, approximating a    resin content of 38% in the final assembly, was cast onto a release    paper using a hot roll coater.

Preparation of the Hardener Component:

-   4. A 3.3% solution of 2PZ imidazole in acetone was prepared. This    solution concentration ensured that a nominal 20 g of reactive    curative was incorporated in each square meter of fabric.-   5. An 840 gsm glass fabric was passed through a bath containing the    solution from step 4 and subsequently through two ovens to evaporate    off the solvent.-   6. Finally, the film prepared in step 3 was lightly tacked onto the    surface of the 2PZ-impregnated fabric, ensuring minimum impregnation    into the fabric. A polyethylene or silicone coated release paper may    be placed as a protector layer on one or both sides of the assembly.    The assembly may be supplied in rolls or as cut sheets.

The out-life of this assembly was determined over a 14-day period in asimilar manner to that described in Example 1. Assemblies were cured for15 minutes at 110° C. and the Tg (determined by DMA) and visual aspectof the laminates were observed. The data outlined below indicated thatthe out-life was a minimum of 14 days and may be longer.

No. of Days @ Room Tg (° C.) Temperature Ext. onset E′  0 (as made) 114 7 112 14 115

Assemblies of the types described above show comparable mechanicalproperties such as peel when compared with conventional prepreg(reinforcement fully impregnated with a homogenous matrix resin).

In order that the present invention is understood it will now bedescribed by way of example only with reference to the accompanyingdrawings in which, FIG. 1 shows an uncured bi-layer assembly 10comprising a reinforcement layer 1 that includes the reinforcingmaterial (fibers) shown schematically at 12 and the reactive curingagent. The uncured assembly 10 further includes a matrix layer 2 thatcontains the matrix resin and a latent curing agent. As shown by thephantom line 13, the matrix layer 2 impregnates the reinforcement layer1 by 15% or less.

FIG. 2 shows an uncured multi-layer assembly 20 that comprises twomatrix layers 3 and 5 that each contains resin and a latent curingagent. A reinforcement layer 5 is located between the two resin matrixlayers 3 and 5. The reinforcement layer 5 includes an optional surfacefleece layer 5 b and one or more plies of reinforcing material (fibers)as shown schematically at 5 a. The reinforcement layer 5 also includes areactive curing agent that may be distributed throughout thereinforcement layer 5 or located only in the layer 5 a of reinforcingmaterial. The matrix layers 3 and 4 can be the same or different and thelatent curing agent(s) can be present in the two layers in differingamounts. Phantom lines 14 and 15 show the depth of impregnation of thematrix resin layers 3 and 5 into the reinforcement layer 5. As mentionedpreviously, the impregnation should be less than 15%.

FIG. 3 shows the assembly 10 after it has been cured to form a snowboardor ski 30. The matrix layer 2 has completely impregnated thereinforcement layer 1 to provide cured composite structure. Likewise,FIG. 4 shows the assembly 20 after it has been cured to form a snowboardor ski 40. The matrix layers 3 and 4 have completely impregnated thereinforcement layer 5 to provide the cured composite structure

It is of course to be understood that the invention is not intended tobe restricted the details of the above embodiment, which is describedonly by way of example.

1. An uncured fiber reinforced assembly comprising: a reinforcementlayer having a first surface and a second surface that define thethickness of said reinforcement layer, said reinforcement layercomprising a fibrous material and at least one highly reactive curingagent; and a matrix film layer applied to at least part of said first orsecond reinforcement layer surfaces wherein said matrix film layercomprises at least one uncured epoxy resin and at least one latent epoxycuring agent and wherein said matrix film layer does not substantiallyimpregnate said reinforcement layer.
 2. An uncured fiber reinforcedassembly according to claim 1 wherein said matrix film layer impregnatesthe reinforcement layer by less than 10% of the thickness of saidreinforcement layer.
 3. An uncured fiber reinforced assembly accordingto claim 2 wherein said matrix film layer impregnates the reinforcementlayer by less than 5% of the thickness of said reinforcement layer. 4.An uncured fiber reinforced assembly according to claim 1 wherein saidmatrix film layer has a minimum viscosity of 100 Pas at ambienttemperature.
 5. An uncured fiber reinforced assembly according to claim1 wherein said fibrous material is selected from the group of fibersconsisting of synthetic fibers, natural fibers, hybrid fibers, mixedfibers, stretch-broken fibers and selectively discontinuous fibers. 6.An uncured fiber reinforced assembly according to claim 1 wherein saidmatrix film layer comprises one or more additional ingredients selectedfrom the group consisting of flexibilizers, toughening agents,accelerators, thermoplastics, core shell rubbers, flame retardants,wetting agents, pigments/dyes, ultra-violet absorbers, anti-fungalcompounds, fillers, toughening particles and viscosity modifiers.
 7. Acomposite structure comprising an uncured fiber reinforced assemblyaccording to claim 1 that has been cured to form said compositestructure.